1. Field of the Invention
This invention relates to balloon catheters such as intra-aortic balloon catheters and pulmonary arterial balloon catheters. More particularly, the invention concerns an apparatus for wrapping a balloon catheter before the catheter is inserted into a patient. More specifically, the invention is directed to improved wrapping of intra-aortic balloon catheters.
2. Background Description
The use of balloon catheters in medicine is known. One of these balloon catheters is an intra-aortic balloon catheter.
An intra-aortic balloon catheter is utilized in balloon pumping and consists primarily of two segments: the balloon chamber or balloon, and the catheter tube. The catheter tube is a long thin hollow flexible tube, one end of which is fed into an artery of a patient and the other end of which remains outside the body. The balloon, which is sausage shaped, consists of a membrane attached to the end (distal) of the catheter tube that goes into the body. The end that remains outside the body (proximal) is equipped for connection to an external pump console. The console pumps gas, usually helium, through the catheter tube into the balloon.
The balloon membrane of an intra-aortic balloon catheter is not distensible. It does not stretch or contract but has a constant surface area irrespective of whether it is in its inflated or collapsed state.
In use, the balloon of the device is maneuvered by a physician so that it is positioned in the descending aorta, the major artery leading from the left ventricle of the heart to the other organs of the body. It is normally inserted into the body, however, through the femoral artery, which is located in the groin area of the thigh. From there, by pushing on the catheter tube itself, the physician can feed the balloon up through the arterial system until it reaches the aorta.
The balloon is then inflated and deflated again and again, out of phase with the natural pumping action of the heart. That is, immediately after the heart relaxes following a pump cycle, the balloon is inflated and just before the heart begins the next pumping action the balloon is deflated. This process is often called "counterpulsation."
The timing of the inflate/deflate cycle is controlled by the patient's electro-cardiogram or arterial blood pressure so that it is properly synchronized to the patient's natural heart rhythm. When the balloon is inflated, it forces blood out of the portion of the aorta where the balloon is located. In so doing, the inflation of the balloon causes a second pumping action, supplementing the natural pumping action of the heart. In particular, it forces extra oxygen-containing blood through the coronary arteries, thereby providing additional nourishment to the heart. Thereafter, when the balloon is deflated, the pressure in the aorta is lowered. Since there is then much less back pressure against which the heart must pump, the exertion of the heart muscle during the next pumping cycle is substantially reduced.
The intra-aortic balloon catheter is a temporary assist device, typically being left in the patient for about three days. It is frequently used after open-heart surgery to help wean a patient off a heart-lung machine. It is often used for patients suffering from cardiogenic shock, myocardial infraction and acute angina pectoris and is frequently used to sustain patients who might not otherwise be able to sustain themselves until permanent treatment can be affected.
The original intra-aortic balloon catheters were inserted by surgeons via a surgical procedure. The femoral artery was surgically exposed by making an incision in the groin. A second incision then was made in the artery, a graft was sewn in and the IAB inserted. Removal of the device requires surgery as well.
In surgical balloon catheters, the catheter tube itself ran the entire length of the balloon. In other words, the far (distal) end of the balloon was fixedly secured to the far end of the catheter tube and the near (proximal) end of the balloon was also fixedly secured to the catheter tube.
Today most intra-aortic balloons are inserted by cardiologist without the need for surgery. These intra-aortic balloon catheters are inserted by puncturing the artery with a needle instead of using a surgical incision. This procedure is called a percutaneous insertion. See Seldinger, Catheter Replacement of the Needle in Percutaneous Arteriography, Acta Radiol (Stockholm, Sweden), 39:368 (1953).
In percutaneous insertion, the patient is given a local anesthetic, after which a small incision is made in the skin over the femoral artery. A hypodermic needle then is used to puncture the femoral artery. The needle is replaced by a guide wire, over which is inserted a sheath. The percutaneous intra-aortic balloon catheter is introduced into the artery through the sheath.
The smaller the diameter or profile of the balloon catheter as it was being inserted into the femoral artery and being fed up into the aorta, the better. Making this entering profile small, however, has presented difficulties because the non-distensible balloon membrane does not contract when deflated.
Since the membrane of an intra-aortic balloon does not contract, some other methods were employed to make the entering profile as small as possible. With surgical intra-aortic balloons this was accomplished by bunching or wrapping the balloon membrane around the catheter tube within it. Because the catheter tube was within the balloon, however, no matter how tightly bunched the balloon could not be made any smaller than the tube itself.
In the early percutaneous intra-aortic balloon catheters, the profile of the balloon was further reduced by instead of attaching both ends of the balloon to the catheter tube, attaching only the proximal end of the balloon to it. Then a very thin rod or support member ran from the tip of the balloon through the balloon and terminated in the catheter tube.
The support member also was rotatably coupled to the catheter tube at the proximal end of the balloon so that the other end of the balloon could be twisted relative to the proximal end. By permitting the support member to rotate, it was possible, after evacuating air from the balloon to twist the balloon membrane into a spiral wrap about the support member.
Because the support member was much thinner than the catheter tube when the balloon was wrapped about the support member, it thus was made to have a diameter as small as that of the catheter tube. Since the physician guided the wrapped balloon catheter up to the aorta by pushing on the catheter tube, a disc shaped keeper preventing the support member from sliding or telescoping into the catheter tube was added, thereby permitting the pushing force to be transmitted from the catheter tube through the support member and to the balloon tip.
Certain difficulties were experienced with these early percutaneous intra-aortic balloon catheters. Since the balloon was wrapped after placing a vacuum on the balloon catheter and manually rotating the support member, the resulting spiral on the balloon tended to be uneven and non uniform. Often the balloon was over-wrapped by rotating excessively thus inducing torsional stress and fatigue on the balloon and creating a potential for the balloon to rupture in the patient during subsequent balloon inflation and deflation. Moreover, the early percutaneous intra-aortic balloon catheters were unwapped in the aorta of the patient by removing the vacuum previously placed on the balloon catheter. Due to the characteristics of the balloon material this allegedly permitted the balloon and its attached support member to unwind and return to their original unwrapped condition. There, however, was no accurate way to make certain that the balloon fully unwrapped in the aorta. Should the balloon not unwrap fully, proper counter-pulsation could not be achieved. The balloon catheter would have to be removed and a new balloon catheter inserted.
In later percutaneous intra-aortic balloon catheters, inter alia, the support member was completely modified from the early percutaneous devices so that it ran from the balloon tip, through the balloon and catheter tube and terminated in a rotatable wrap handle. By rotating the wrap handle, torsional forces were transmitted to the attached support member which in turn caused rotation of the balloon about the support member thereby reducing the balloon profile. The wrap handle included stops which prevented rotation of the handle and the attached support member by more than a predetermined number of rotations in either rotational direction. When the wrap handle was fully rotated in one direction and contacted a stop, the balloon would be completely wrapped but when fully rotated in the opposite direction until it contacted the other stop, the balloon would be completely wrapped. The wrap handle of these latter percutaneous intra-aortic balloon catheters provided positive controlled wrapping and unwrapping of the balloon from outside the patient. The use of the wrap handle eliminated the problems associated with the early percutaneous intra-aortic balloon catheters.
The present invention constitutes a further improvement in the technique of wrapping an intra-aortic balloon catheter. With the present invention, a wrap handle is no longer necessary to achieve positive controlled wrapping and unwrapping yet the problems associated with the early percutaneous balloon catheters not having wrap handles still are avoided.